Clinically, vocal hyperfunction has not only been associated with glottal-related variables but also with supraglottic tissue displacement or supraglottic activity. The latter is still one of the basic paradigms for evaluation of laryngeal hyperfunction in some places in the world. ^{1, 2} Supraglottic activity is defined as the laryngeal movement/displacement just above the true vocal folds. ² Two main expressions of supraglottic activity may occur during voice production. ³ An anterior-posterior (A-P) supraglottic narrowing is observed when there is a reduction of the distance between the arytenoid cartilages and the epiglottal petiole, producing a partial or complete view obstruction of the vocal folds in an anterior to posterior direction.  Medial displacement occurs when the false vocal folds (ventricular folds) adduct producing a partial or complete impediment to easily observe the true vocal folds. These two manifestations of supraglottic tissue mobilization may occur either isolated (only one can be observed) or together. Supraglottic activity is usually associated by some clinicians with hyperfunctional voice disorders and is considered to reflect vocal misuse. ^1-6Even if both medial and A-P narrowing are deemed as endoscopic signs of vocal hyperfunction, some studies have observed that supraglottic activity may also be present in normal speaking ^{1, 2 6-8} and singing ^9-14 voice production.

The subjective visual assessment of supraglottic activity is performed by clinicians commonly without controlling any of the variables that might possibly influence the degree of this tissue displacement during phonation. A series of studies have been performed to explore how supraglottic activity can be modified by several variables such as vocal intensity, fundamental frequency, voice classification, singing style, voice training, and type of phonatory tasks. ^{10, 12, 14} All these studies have reported in general that both A-P and medial narrowing (and even pharyngeal narrowing) increase with the intensity and fundamental frequency. This relationship has been observed not only in professional voice users (opera singers, CCM singers, actors/actresses, and rock singers), but also in non-trained participants with normal voice and people with voice disorders. ¹⁵ In all these groups, the vocal tract tends to react in the same way when vocal intensity and fundamental frequency are increased. Moreover, some data have shown that vocally trained participants had a higher degree of both laryngeal and pharyngeal narrowing, as compared with normal untrained participants. ⁸

Even though some studies have suggested that people with voice disorders may present a greater degree of A-P and medial laryngeal narrowing, ^{1, 3-6} these studies have not controlled variables that influence the degree of tissue displacement (Intensity, fundamental frequency, etc.). A recent study reported no significant differences between female participants (non-vocally trained) with normal voices and disordered voices (moderate and severe) on supraglottic laryngeal and pharyngeal activity as observed endoscopically. In this study, vocal intensity and pitch were controlled and they showed the same effect on supraglottic activity observed previously in singers: the higher the vocal intensity and fundamental frequency, the narrower is the larynx and pharynx. ¹⁵ A comparison of supraglottic activity between vocally trained healthy singers (belters) and subjects diagnosed with dysphonia showed various similarities between both groups: high vertical larynx position, small hypopharyngeal width, and small epilaryngeal outlet. ¹⁶

At first glance, the association between loudness level and laryngeal/pharyngeal narrowing previously found may be linked with a possible hyperfunctional reaction of supraglottic structures caused by an effortful phonation when producing a loud and high pitch voice. This reaction may be superficially interpreted as potentially harmful to the phonatory mechanism. However, as mentioned above, greater supraglottic activity has also been associated with louder voice among normal well-trained professional voice users. ^{10, 12, 14} Therefore, it could also be the case that supraglottic activity contributes to loudness level, vocal brilliance, high pitches, and easy voice production. ^{10, 17, 18} Moreover, greater supraglottic activity during loud phonation might not only be considered as a normal trait, but also a desirable one, perhaps even being a protecting factor for both normal and disordered voices. An A-P narrowing of epilaryngeal tube has been reported to positively impact vocal fold oscillation and vocal fold adduction. ^19-21 This narrowing has been associated with greater source-filter interaction and higher vocal tract inertance, which promote a more resonant voice quality, easier voice production, and more economic voicing. ^17-19 Additionally, some semioccluded vocal tract exercises (e.g., tube phonation in air or in water) have been associated with a narrower epilaryngeal tube in vocally healthy people, with greater effect during phonation with higher airflow resistance exercises (e.g., narrow stirring straws and tubes submerged deep into water). Maximum power transfer and impedance matching could be related to these findings. ^{22, 23}

Although all this is already well known by some specialized/experienced clinicians and researchers, there are still people who associate supraglottic tissue displacement (narrowing) with vocal hyperfunction.  To sum up, current data suggest that the presence and degree of supraglottic activity is not necessarily higher among patients with dysphonia when compared to normal voice participants. Loudness level and pitch, among other variables, clearly impact the degree of tissue displacement of supraglottic structures, both among normal voice participants and participants with voice disorders. Thus, loudness and pitch are variables that need to be controlled when performing laryngoscopic examinations, whether in clinical or research contexts, to establish more reliable conclusions. Finally, it could be questioned if supraglottic narrowing should really be associated with detrimental vocal behavior (either as cause or consequence) or a natural and even desirable compensatory action to protect the vocal folds and to promote a healthier vocal technique.

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